The present invention relates to remote control devices for controlling the operation of broadcast receivers, and relates particularly to ultrasonic devices of this type.
There exists in commerce a constantly increasing demand for ultrasonic remote-control devices for controlling broadcast receivers, for example television sets. Such devices are employed to control, from a distance, various functions, such as, for example, switching on and off, channel selection, volume adjustment, etc. For this purpose it is necessary to provide an ultrasonic transmitter as well as an ultrasonic receiver. When the key, or button, on the ultrasonic transmitter corresponding to the desired function is actuated, the transmitter emits ultrasonic oscillations which contain the control instruction required for effecting the desired operating function and which are received and appropriately evaluated by the ultrasonic receiver.
However, remote control with ultrasonic devices is difficult in that interferences may occur in the transmission path, the path over which ultrasonic waves travel from the transmitter to the receiver, so that the received ultrasonic oscillations do not coincide with the transmitted oscillations. Such interference may be, for example, that the received ultrasonic oscillation temporarily has too low an amplitude so that it cannot be evaluated by the ultrasonic receiver. As a result, errors in switching occur and a function other than the desired one, or no operating function at all, is performed.